The development of mobile internet has triggered an explosion of mobile data traffic. New services and applications, such as Internet of Things, machine communications, Internet of Vehicles and control networks, also put forward relatively high requirements on wireless communications in terms of time delay and reliability. To meet these challenges, academia and industry have proposed the International Mobile Telecommunications (IMT)-2020 plan to study the fifth generation mobile communication technology, i.e., 5G, 5G will greatly improve the performance of the current long term evolution (LTE, Long Term Evolution) system in terms of time delay, capacity, reliability, flexibility, energy consumption, and so on.
5G puts forward a demand of improving the hotspot region capacity as 1000 times as that of 4G Capacity improvement mainly includes three ways of improving frequency efficiency, increasing frequency spectrum and densely deploying cells. At present, the link spectral efficiency is close to a theoretical limit and no consensus has been reached on the uniform allocation of 5G spectrum in the world. Therefore, the improvement of 5G capacity depends on the dense cell deployment to a great extent.
Ultra dense network (UDN, Ultra Dense Network) is proposed in this context, and can be deemed as a further evolution on small cell (Small Cell) enhancement technique. In the UDN network, a density of transmission points (TPs) will be further improved, and the coverage of TP will be further reduced (dozens of meters, and even tens of meters), and each TP may only serve one or several users.
A backhaul link (BL, Backhaul Link) is one key issue to be solved by the UDN, and directly affects the deployment cost, capacity and performance of the UDN. Transmission points in the ultra-dense network may be classified into two categories, i.e., transmission points using a self-backhaul link (sBL, self-Backhaul Link) and transmission points using a non-self-backhaul link (nsBL, non-self-Backhaul Link). The self-backhaul means that the backhaul link uses the same radio transmission technology and frequency band as that of an access link (AL, Access Link). The backhaul link and the access link may be multiplexed by means of time division or frequency division. Transmission points using nsBL connect to a core network by using transmission technologies different from AL, such as wireless local area network (WLAN, Wireless-LAN), asymmetric digital subscriber line (ADSL, Asymmetric Digital Subscriber Line), etc., and media such as fibers and cables, or the like.
For many application scenarios of the UDN (such as dense blocks), the cost of deploying a wired BL (such as deployment or rental costs of cables or fibers, selection and maintenance costs of site positions, etc.) is often unacceptable and unplanned deployments cannot be implemented. In addition, if the wired BL is provided at the maximum system capacity, the utilization rate of the BL will be very low, which seriously wastes the investment costs. This is because: (1) in the case of dense deployment of TPs, each transmission point serves relatively few users, and the load fluctuates greatly; (2) for the consideration of energy saving or control interference, some TPs will be opened or closed passively; therefore, the BL is often in an idle state; and (3) content prediction and cache technologies increase the fluctuation of resource demands on the BL.
Microwaves are often used as backhaul links for a macro base station, but there are many limitations to use the microwaves in the UDN. On one hand, the microwaves may increase the hardware cost of low power transmission points. Different from the macro base station, a low power TP in the UDN has a lower cost, and microwave hardware contributes more to the hardware cost of the entire transmission point. Secondly, the microwaves may also increase an additional frequency spectrum cost. If an unlicensed frequency spectrum is used, it is often very difficult to control interference, so that the transmission quality of BL cannot be guaranteed. More importantly, the antenna height of TP is relatively low in the major scenario of the UDN, so that the microwaves are blocked easily, which causes the violent fluctuation of the quality of BL.
The above analysis shows that sBL is very attractive in the UDN. It does not require wired connections, supports unplanned or semi-planned TP deployment, and effectively reduces the deployment costs. The frequency spectrum and hardware costs can be reduced by sharing the frequency spectrum with AL and wireless transmission technologies. Through the joint resource allocation between AL and BL, the system can adaptively adjust the resource allocation ratio according to the network load conditions, so as to improve the resource utilization. In addition, through the joint optimization with AL, the quality of the wireless self-backhaul link can be effectively guaranteed, and the transmission reliability can be greatly improved. Using the sBL technology means that multiple hop transmission is needed from the first sending point to the last receiving point (terminal). FIG. 1 is a schematic diagram of using two-hop transmission. As shown in FIG. 1, the core network (CN, Core Network) communicates with a user equipment (UE, User Equipment) through a donor transmission point (donorTP) and a relay transmission point (relayTP).
The method for transmitting a signal in the related art substantially includes:
receiving and/or sending, by a transmission point, a signal and/or data in a time unit.
As shown in Table 1, the time unit includes: a downlink control area (Control (DL)), a data area (Data(Tx)), a guard period (GP, Guard Period) and an uplink control area (Control (UL)).
TABLE 1Control (DL)Data (Tx)GPControl (UL)
This section provides background information related to the present disclosure which is not necessarily prior art.